Inkjet recording method

ABSTRACT

The inkjet recording method includes ejecting an inkjet ink toward a recording medium to form an ink image on the recording medium. The inkjet ink includes a pigment, water, a surfactant, and a compound having a formula (1) CH 3 OCH 2 CH 2 CON(CH 3 ) 2 , and optionally includes a compound having a formula (2) CH 3 CH 2 CH 2 CH 2 OCH 2 CH 2 CON(CH 3 ) 2 . The inkjet recording method satisfies a relation, 16≦γ cos θ≦26, wherein γ represents the surface tension of the inkjet ink in units of mN/m, and θ represents the angle of contact of the inkjet ink with the recording medium in units of degree measured 0.1 seconds after dropping an droplet of the inkjet ink with a volume of 2.5 μl on the recording medium.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. §119 to Japanese Patent Application No. 2012-020343 filed on Feb.1, 2012 in the Japan Patent Office, the entire disclosure of which ishereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to an inkjet recording method.

BACKGROUND OF THE INVENTION

Since inkjet printers have low costs and can easily produce colorimages, inkjet printers have been rapidly spreading. Recently, there isa need for an inkjet printer capable of producing high quality images.

With respect to inkjet ink, an aqueous ink composition including apigment, water, an organic solvent, a resin and a surface tensionadjuster for inkjet ink compositions is disclosed. In this regard, theorganic solvent of the ink composition is a compound having thefollowing formula:R¹OCH₂CH₂CONR²R³wherein R¹ represents an alkyl group having 1 to 8 carbon atoms, andeach of R² and R³ independently represents a hydrogen atom, an alkylgroup having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbonatoms and including an ether bond therein.

The total content of water and the organic solvent is from 10% to 49% byweight based on the weight of the ink composition.

However, it is difficult for the ink composition to form images having ahigh image density and including no blurred character images on a plainpaper. Specifically, when high density images are formed by such an inkcomposition, character images are blurred. In contrast, when characterimages without blurring are formed by such an ink composition, the imagedensity is low.

For these reasons, the inventors recognized that there is a need for aninkjet recording method, by which high density images can be formed on aplain paper without forming blurred character images.

BRIEF SUMMARY OF THE INVENTION

As an aspect of the present invention, an inkjet recording method isprovided which includes ejecting an inkjet ink toward a recording mediumto form an ink image on the recording medium. The inkjet ink includes apigment, water, a surfactant, and a compound having the followingformula (1):CH₃OCH₂CH₂CON(CH₃)₂   (1).The inkjet ink optionally includes another compound having the followingformula (2)CH₃CH₂CH₂CH₂OCH₂CH₂CON(CH₃)₂   (2).

The inkjet recording method satisfies the following relation:16≦γ cos θ≦26,wherein γ represents the surface tension of the inkjet ink in units ofmN/m, and θ represents the angle of contact of the inkjet ink with therecording medium in units of degree measured 0.1 seconds after droppingan droplet of the inkjet ink with a volume of 2.5 μl on the recordingmedium.

The aforementioned and other aspects, features and advantages willbecome apparent upon consideration of the following description of thepreferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an inkjet recording apparatusfor use in the inkjet recording method of the present invention;

FIG. 2 is a side view of the inkjet recording apparatus illustrated inFIG. 1;

FIG. 3 is a partial enlarged view illustrating the inkjet recording headof the inkjet recording apparatus illustrated in FIG. 1; and

FIG. 4 is a schematic view illustrating the ink cartridge of the inkjetrecording apparatus illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the inkjet recording method of the present inventionwill be described by reference to drawings.

The inkjet recording method of the present invention includes ejectingan inkjet ink toward a recording medium to form an image on therecording medium.

The inkjet ink includes a compound having formula (1) (i.e.,3-methoxy-N,N-dimethylpropionamide) or a combination of the compoundhaving formula (1) and another compound having formula (2) (i.e.,3-n-butoxy-N,N-dimethylpropionamide), and a pigment, water and asurfactant.

When the surface tension of the inkjet ink is γ[mN/m], and the angle ofcontact of the inkjet ink with the recording medium measured 0.1 secondsafter dropping an droplet of the inkjet ink with a volume of 2.5 μl onthe recording medium is θ[°], the following relation is preferablysatisfied:16≦γ cos θ≦26.

When γ cos θ is less than 16, the image density of images formed onplain papers tends to decrease. When γ cos θ is greater than 26, blurredcharacter images tend to be formed on plain papers.

In this application, the surface tension γ of an inkjet ink is measuredat 25° C. and 50% RH using an automatic surface tensiometer CBVP-Z fromKyowa Interface Science Co., Ltd.

In addition, the contact angle θ is measured at 25° C. and 50% RH usingan automatic contact angle measuring instrument OCAII200 from DataPhysics Corp.

In general, the following Lucas-Washburn equation is well known as anequation representing penetration of a liquid.L=(r γ cos θ·t/2η)^(1/2)wherein L represents the penetration depth of the liquid, r representsthe radius of the capillary, t represents time, η represents theviscosity of the liquid, γ represents the surface tension of the liquid,and θ represents the contact angle of the liquid. It is clear from theequation that as γ cos θ increases, the liquid penetrates more deeply,and as γ cos θ decreases, the liquid penetrates less deeply.

Since the inkjet ink used for the inkjet recording method of the presentinvention includes 3-methoxy-N,N-dimethylpropionamide or a combinationof 3-methoxy-N,N-dimethylpropionamide and3-n-butoxy-N,N-dimethylpropionamide, γ cos θ can be controlled so as tofall in the range of from 16 to 26.

In this regard, the plain paper used for the inkjet recording method ofthe present invention can include used paper and/or a sizing agent.

The compound (1), 3-methoxy-N,N-dimethylpropionamide, has a relativelyhigh boiling point of 216° C., a relatively high equilibrium moisturecontent of 39.2% by weight at 23° C. and 80% RH, and a relatively lowviscosity of 1.4 mPa·s at 25° C. In addition, since the compound (1) canbe easily dissolved in water, the viscosity of the resultant inkjet inkcan be decreased. Since the compound (2),3-n-butoxy-N,N-dimethylpropionamide, also has a relatively lowviscosity, the viscosity of the resultant inkjet ink can be decreased.In addition, the compound (1) and a combination of the compounds (1) and(2) can enhance the wetting property of the inkjet ink on plain papers.

The total content of 3-methoxy-N,N-dimethylpropionamide and3-n-butoxy-N,N-dimethylpropionamide in the inkjet ink is generally from10% to 20% by weight, and preferably from 18% to 20% by weight. When thetotal content is less than 10% by weight or greater than 20% by weight,the image density of images formed by the inkjet ink tends to decrease.

The surfactant to be included in the inkjet ink is not particularlylimited as long as the surfactant can improve the leveling property ofthe ink. Suitable materials for use as the surfactants includefluorine-containing surfactants, silicone surfactants, and anionicsurfactants, nonionic surfactants. These surfactants can be used aloneor in combination. Among these surfactants, fluorine-containingsurfactants are preferable.

The number of carbon atoms having a fluorine atom in suchfluorine-containing surfactants is generally from 2 to 16, andpreferably from 4 to 16. When the number of carbon atoms having afluorine atom is less than 2, the leveling property of the resultant inktends to deteriorate. When the number is greater than 16, the ejectionproperty of the resultant ink tends to deteriorate.

Specific examples of fluorine-containing anionic surfactants includeperfluoroalkylsulfonic acids, salts of perfluoroalkylsulfonic acids,perfluoroalkylcarboxylic acids, salts of perfluoroalkylcarboxylic acids,salts of perfluoroalkylphosphates, and salts of sulfates ofpolyoxyalkylene ethers having a perfluoroalkyloxy group in a side chainthereof.

Specific examples of the counter ions of these fluorine-containinganionic surfactants include a lithium ion, a sodium ion, a potassiumion, an ammonium ion, a monoethanolammonium ion, a diethanolammoniumion, and a triethanolammonium ion.

Among these fluorine-containing anionic surfactants, compounds havingone of the following formulae (1)-(4) are preferable.

In formula (1), Rf represent a group having the following formula (A) or(B).

In formula (1), A represents a group having one of the followingformulae.—SO₃ ⁻M⁺, —COO⁻M⁺, and —PO₃ ⁻M⁺wherein M⁺ represents a proton, a lithium ion, a sodium ion, a potassiumion, an ammonium ion, a monoethanolammonium ion, a diethanolammoniumion, and a triethanolammonium ion.(RfO)_(n)PO(O⁻M⁺)_(m)   (2)

In formula (2), M⁺ is defined above, n is an integer of from 3 to 10,and Rf′ represents a group having the following formula (C).F(CF₂CF₂)_(n)CH₂CH₂—  (C)Rf′SCH₂CH₂COO⁻M⁺  (3)

In formula (3), M⁺ is defined above, and Rf′ represents a group havingthe above-mentioned formula (C).Rf′SO₃ ⁻M⁺  (4)

In formula (4), M⁺ is defined above, and Rf′ represents a group havingthe above-mentioned formula (C).

Specific examples of fluorine-containing nonionic surfactants includeperfluoroalkyl phosphates, perfluoroalkylethylene oxide adducts, andpolyoxyalkylene ethers having a perfluoroalkyloxy group in a side chainthereof Among these compounds, polyoxyalkylene ethers having aperfluoroalkyloxy group in a side chain thereof are preferable becauseof hardly foaming.

Among such polyoxyalkylene ethers compounds, compounds having one of thefollowing formulae (5)-(7) are preferable.CF₃CF₂(CF₂CF₂)_(m)CH₂CH₂O(CH₂CH₂O)_(n)H   (5)wherein m is 0 or an integer of from 1 to 10, and n is 0 or an integerof from 1 to 40.RfO(CH₂CH₂O)_(n)H   (6)wherein Rf represents a group having the above-mentioned formula (A) or(B), and n is an integer of from 5 to 20.Rf′O(CH₂CH₂O)_(n)H   (7)wherein Rf′ represents a group having the above-mentioned formula (C),and n is an integer of from 1 to 40.

Fluorine-containing ampholytic surfactants having the following formula(8) can also be preferably used.

wherein Rf represents a group having the above-mentioned formula (A) or(B).

In addition, oligomer type fluorine-containing surfactants having thefollowing formula (9) or (10) can also be preferably used.

In formula (9), M⁺ is defined above, and Rf′ represents a group havingthe following formula (D):F(CF₂CF₂)_(n)CH₂—  (D)wherein n is an integer of from 1 to 4.

In formula (10), Rf′ represents a group having the above-mentionedformula (D), and each of k, m and n is independently an integer of from1 to 10.

Marketed fluorine-containing surfactants can be used. Specific examplesthereof include SARFRONs S-111, S-112, S-113, S-121, S-131, S-132, S-141and S-145, which are manufactured by Asahi Glass Co., Ltd.; FLUORADsFC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430 and FC-431, whichare manufactured by Sumitomo 3M Ltd.; MEGAFACEs F-470, F-1405 and F-474,which are manufactured by DIC Corp.; ZONYLs TBS, FSP, FSA, FSN-100, FSN,FSO-100, FSO, FS-300 and UR, which are manufactured by Du Pont; FT-110,FT-250, FT-251, FT-400S, FT-150 and FT-400SW, which are manufactured byNeos Co., Ltd.; and POLYFOX PF-151N, which is manufactured by Om NovaSolutions, Inc.; and UNIDYNE DSN-403N from Daikin Industries, Ltd.

The silicone surfactant mentioned above for use in the inkjet ink is notparticularly limited. Suitable materials for use as the siliconesurfactant include polydimethylsiloxane whose side chains are modified,polydimethylsiloxane whose both ends are modified, polydimethylsiloxanewhose one end is modified, and polydimethylsiloxane whose both ends andside chains are modified. Among these surfactants, polyether-modifiedsilicone surfactants, which have a polyoxyethylene group or apolyoxyethylenepolyoxypropylene group as a modification group, arepreferable.

Among polyether-modified silicone surfactants, compounds having thefollowing formula (11) are preferable.

In formula (11), R represents an alkylene group, R′ represents an alkylgroup, and each of m, n, a and b is independently an integer.

Specific examples of marketed products of such polyether-modifiedsilicone surfactants include KF-618, KF-642 and KF-643 from Shin-EtsuChemical Co., Ltd.

Any known anionic surfactants can be used for the inkjet ink, andpolyoxyethylene alkyl ether acetates, dodecylbenzene sulfonates,laurates, and polyoxyethylene alkyl ether sulfates are preferably used.

Any known nonionic surfactants can be used for the inkjet ink, andpolyoxyethylene alkyl ethers, polyoxypropylene polyoxyethylene alkylethers, polyoxyethylene alkyl esters, polyoxyethylene sorbitan fattyacid esters, polyoxyethylene alkylphenyl ethers, polyoxyethylenealkylamines, and polyoxyethylene alkylamides are preferably used.

The content of such a surfactant in the inkjet ink is preferably from0.01% to 3% by weight, and more preferably from 0.5% to 2% by weight,based on the total weight of the inkjet ink. When the content is lessthan 0.01% by weight, the leveling property of the inkjet ink is hardlyenhanced. In contrast, when the content is greater than 3% by weight,the image density tends to decreases.

Organic pigments and inorganic pigments can be used as the pigment to beincluded in the inkjet ink. In this regard, a dye can be used incombination with a pigment to adjust the color tone of the ink.

Specific examples of the inorganic pigments include, but are not limitedthereto, titanium oxide, iron oxide, calcium carbonate, barium sulfate,aluminum hydroxide, barium yellow, cadmium red, chrome yellow, andcarbon black.

The preparation method of carbon black is not particularly limited, andfor example, contact methods, furnace methods, and thermal methods canbe used.

Specific examples of the organic pigments include, but are not limitedthereto, azo pigments such as azo lakes, insoluble azo pigments,condensed azo pigments, and chelated azo pigments; polycyclic pigmentssuch as phthalocyanine pigments, perylene pigments, perynone pigments,anthraquinone pigments, quinacridone pigments, dioxazine pigments,indigo pigments, thioindigo pigments, isoindolinone pigments, andquinophthalone pigments; chelated dyes such as basic dye-type chelates,and acidic dye-type chelates; nitro pigments, nitroso pigments, andAniline Black. Among these pigments, azo pigments and polycyclicpigments are preferable.

The color of the pigment is not particularly limited, and one or morepigments for forming black color and chromatic colors are used so thatthe resultant ink has the target color.

Specific examples of black color pigments include carbon blacks (i.e.,C.I. Pigment Black 7) such as furnace black, gas black, lamp black,acetylene black, and channel black; powders of metals (i.e., C.I.Pigment Black 11) such as copper and iron; metal oxides such as titaniumoxide; and organic pigments such as Aniline Black (i.e., C.I. PigmentBlack 1).

Specific examples of chromatic color pigments include C.I. PigmentYellows 1, 3, 12, 13, 14, 17, 24, 34, 35, 37, 42 (yellow iron oxide),53, 55, 74, 81, 83, 95, 97, 98, 100, 101, 104, 108, 109, 110, 117, 120,128, 138, 150, 151, 153 and 183; C.I. Pigment Oranges 5, 13, 16, 17, 36,43 and 51; C.I. Pigment Reds 1, 2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2(permanent red 2B(Ca)), 48:3, 48:4, 49:1, 52:2, 53:1, 57:1 (BrilliantCarmine 6B), 60:1, 63:1, 63:2, 64:1, 81, 83, 88, 101 (red iron oxide),104, 105, 106, 108 (cadmium red), 112, 114, 122 (quinacridone magenta),123, 146, 149, 166, 168, 170, 172, 177, 178, 179, 185, 190, 193, 209 and219; C.I. Pigment Violets 1 (Rhodamine Lake), 3, 5:1, 16, 19, 23 and 38;C.I. Pigment Blues 1, 2, 15 (Phthalocyanine Blue), 15:1, 15:2, 15:3(Phthalocyanine Blue), 16, 17:1, 56, 60 and 63; and C.I. Pigment Greens1, 4, 7, 8, 10, 17, 18 and 36.

The pigment included in the inkjet ink is preferably a pigment having aself-dispersing property which can be dispersed in water without using apigment dispersant. Such a pigment having a self-dispersing property ishereinafter referred to as a self-dispersing pigment.

Self-dispersing pigments having a volume average particle diameter (D50)of from 0.01 μm to 0.16 μm are preferably used for the inkjet ink.

Self-dispersing pigments having an ionic group (anionic or cationicgroups) on the surface thereof are preferably used.

Specific examples of the anionic groups of self-dispersing pigmentsinclude, but are not limited thereto, —COO⁻M⁺, —SO₃ ⁻M⁺, —PO₃H⁻M⁺, and—PO₃ ²⁻M⁺ ₂, wherein M⁺ represents a proton, an alkali metal ion, anammonium ion, or an organic ammonium ion.

Specific examples of the alkali metal ion include lithium, sodium andpotassium ions.

Specific examples of the organic ammonium ion include mono- totri-methylammonium ions, mono- to tri-ethylammonium ions, and mono- totri-methanolammonium ions.

Specific examples of the method for forming such an anionic group on thesurface of a pigment include a method in which a pigment is subjected toan oxidation treatment using sodium hydrochlorite; a method in which apigment is sulfonated; and a method in which a pigment is reacted with adiazonium salt.

Specific examples of the cationic groups of self-dispersing pigmentsinclude, but are not limited thereto, the following quaternary ammoniumgroups.

These quaternary ammonium groups are used in combination with a counterion.

Carbon blacks having a surface, to which such a cationic group isbonded, (i.e., self-dispersing carbon blacks) are preferably used forthe inkjet ink for use in the present invention.

The method for preparing carbon black having a cationic group on thesurface thereof is not particularly limited. For example, a method inwhich the surface of a carbon black is treated with3-amino-N-ethylpyridium bromide can be used.

Such self-dispersing pigments can have a configuration such that such anionic group is bonded to the surface thereof with a group therebetween.Specific examples of such an intervening group include alkyl groupshaving 1 to 12 carbon atoms, substituted or unsubstituted phenyl groups,and substituted or unsubstituted naphthyl groups.

The ionic group bonded to the surface of such self-dispersing pigmentswith a group therebetween is not particularly limited, and for example,groups having the following formulae can be used:—CH₂CH₂COO⁻M⁺,wherein M⁻ represents an alkali metal ion, or a quaternary ammonium ion,—R—SO₃ ⁻M⁺,wherein R represents a phenylene group, and M⁺ represents an alkalimetal ion, or a quaternary ammonium ion, and—CH₂CH₂CH₂CH₂CH₂NH₃ ⁺X⁻,wherein X⁻ represents a halogen ion.

The pigment can be dispersed in the inkjet ink using a dispersant.Suitable materials for use as the dispersant include anionicsurfactants, and nonionic surfactants having a HLB of from 10 to 20.

Specific examples of such anionic surfactants include, but are notlimited thereto, polyoxyethylene alkyl ether acetates, alkylbenzenesulfonates (e.g., NH₄, Na, and Ca salts), alkyldiphenyl etherdisulfonates (e.g., NH₄, Na, and Ca salts), sodium dialkylsuccinatesulfonate, sodium salts of formalin condensate of naphthalene sulfonicacid, salts (e.g., NH₄, and Na salts) of sulfuric acid esters ofpolyoxyethylene polycyclic-phenyl ethers, laurates, polyoxyethylenealkyl ether sulfates, and oleates. Among these anionic surfactants,sodium dioctylsulfosuccinate, and ammonium salts (NH₄) ofpolyoxyethylene styrenated-phenyl ether sulfonic acid are preferable.

Specific examples of the above-mentioned nonionic surfactants having aHLB value of from 10 to 20 include, but are not limited thereto,polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers,polyoxyethylene polycyclic-phenyl ethers, sorbitan fatty acid esters,polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkylphenylethers, polyoxyethylene alkylamines, polyoxyethylene alkylamides, andacetylene glycol. Among these surfactants, polyoxyethylene lauryl ether,polyoxyethylene-β-naphthyl ether, polyoxyethylene sorbitan monooleate,and polyoxyethylene styrenated-phenyl ether are preferable.

Such a pigment dispersant is included in the inkjet ink in an amount offrom 0.01 to 1 part by weight, and preferably 0.10 to 0.50 parts byweight, based on 1 part by weight of the pigment included in the inkjetink. When the added amount of such a pigment dispersant is less than0.01 parts, it is often hard to finely disperse the pigment. Incontrast, when the added amount is greater than 1 part, a color bleedingproblem in that different color images, which are adjacent to eachother, are mixed at the boundary portion thereof tends to be caused.

The method for dispersing a pigment is not particularly limited. Forexample, a method including dissolving a dispersant in water, adding apigment thereto, and then dispersing the mixture using a dispersingmachine can be used. Specific examples of such a dispersing machineinclude, but are not limited thereto, high speed agitators such ashomogenizers; dispersing machines using ball media such as bead millsand ball mills; dispersing machines using a shearing force such as rollmills; and ultrasonic dispersing machines.

After performing the dispersing operation, the resultant dispersion ispreferably subjected to filtering using a filter or centrifugalseparator to remove coarse particles therefrom.

Particles of a pigment dispersed in water (in the ink) preferably have avolume average particle diameter (D50) of not greater than 150 nm, andmore preferably not greater than 100 nm. When the volume averageparticle diameter (D50) is greater than 150 nm, the ejection stabilityof the inkjet ink tends to deteriorate.

Particulate resins in which a pigment is dispersed or on which a pigmentis adhered can also be used as the pigment to be included in the inkjetink.

Specific examples of resins constituting the particulate resins include,but are not limited thereto, vinyl resins, polyester resins, andpolyurethane resins. Among these resins, vinyl resins, and polyesterresins are preferable. Specific examples of the resins include theresins described in JP2000-53897A and JP2001-139849 incorporated hereinby reference.

The inkjet ink for use in the present invention can include a wettingagent.

Specific examples of such a wetting agent include polyhydric alcoholssuch as ethylene glycol, diethylene glycol, triethylene glycol,polyethylene glycol, polypropylene glycol, 1,3-butanediol,3-methyl-1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol,2-ethyl-1,3-hexanediol, glycerin, 1,2,6-hexanetriol, 1,2,3-butanetriol,1,2,4-butanetriol, and petriol; alkyl ethers of polyhydric alcohols suchas ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, tetraethylene glycol monomethylether, and propylene glycol monoethyl ether; aryl ethers of polyhydricalcohols such as ethylene glycol monophenyl ether, and ethylene glycolmonobenzyl ether; nitrogen-containing alicyclic compounds such as2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone,1,3-dimethylimidazolidinone, ε-caprolactam, and γ-butyrolactone; amidessuch as formamide, N-methylformamide, and N,N-dimethylformamide; aminessuch as monoethanol amine, diethanol amine, and triethylamine;sulfur-containing compounds such as dimethyl sulfoxide, sulforane, andthiodiethanol; propylene carbonate, and ethylene carbonate. Among thesewetting agents, 3-methyl-1,3-butanediol, 1,3-butanediol, and glycerinare preferable.

The content of such a wetting agent in the inkjet ink is generally from10% to 40% by weight. When the content is less than 10% by weight orgreater than 40% by weight, the ejection stability of the inkjet inktends to deteriorate.

It is preferable that the inkjet ink for use in the present inventionfurther includes a polyol having 8 to 11 carbon atoms and/or a polyolether having 8 to 11 carbon atoms as a penetrant.

The penetrant to be included in the inkjet ink preferably has a watersolubility of from 0.2% to 5.0% by weight at 25° C., and2-ethyl-1,3-hexanediol, which has a water solubility of 4.2% by weightat 25° C., or 2,2,4-trimethyl-1,3-pentanediol, which has a watersolubility of 2.0% by weight at 25° C., is preferably used.

Specific examples of other polyols having 8 to 11 carbon atoms includealiphatic diols such as 2-ethyl-2-methyl-1,3-propanediol,3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1,3-propanediol,2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol,2,5-dimethyl-2,5-hexanediol, and 5-hexene-1,2-diol.

Specific examples of other polyol ethers having 8 to 11 carbon atomsinclude diethylene glycol monophenyl ether, ethylene glycol monophenylether, ethylene glycol monoallyl ether, diethylene glycol monobutylether, propylene glycol monobutyl ether, and tetraethylene glycolchlorophenyl ether.

In addition, lower alcohols such as ethanol can also be used as thepenetrant.

The content of such a penetrant in the inkjet ink is generally from 0.1%to 4.0% by weight. When the content is less than 0.1% by weight, thecolor bleeding problem tends to be caused. In contrast, when the contentis greater than 4.0% by weight, the ejection stability of the inkjet inktends to deteriorate and image density of images recorded by the inkjetink tends to decrease.

The inkjet ink can further include a water-dispersing resin.

Such a water-dispersing resin is present in water as an emulsion such assingle-phase type emulsions, core-shell type emulsions, and power feedtype emulsions.

Specific examples of the resins for use as such a water-dispersing resininclude condensation-type synthetic resins such as polyester resins,polyurethane resins, epoxy resins, polyamide resins, polyether resins,poly(meth)acrylic resins, acrylic-silicone resins, andfluorine-containing resins; addition-type synthetic resins such aspolyolefin resins, polystyrene resins, polyvinyl alcohol resins,polyvinylester resins, polyacrylic acid resins, and unsaturatedcarboxylic acid resins; natural polymeric compounds such as celluloseresins, rosins, and natural rubbers. These resins can be used alone orin combination. Among these resins, polyurethane resins,acrylic-silicone resins, and fluorine-containing resins are preferable.

Among the fluorine-containing resins, fluorine-containing resins havinga fluoro-olefin unit are preferable, fluorine-containing resins having afluoro-olefin unit and a vinyl ether unit are more preferable, andalternate copolymers of a fluoro-olefin and vinyl ether are even morepreferable.

Specific examples of the fluoro-olefin unit include —CF₂CF₂—,—CF₂CF(CF₃)—, and —CF₂CFCl—, but are not limited thereto.

Specific examples of the vinyl ether unit include groups having thefollowing formulae, but are not particularly limited.

Specific examples of marketed products of such water-dispersingfluorine-containing resins include FLUONATEs FEM-500 and FEM-600,DICGUARDs F-52S, F-90, F-90M and F-90N, and AQUAFLAN TE-5A, which aremanufactured by DIC Corp.; and LUMIFLONs FE4300, FE4500 and FE4400, andASAHIGUARDs AG-7105, AG-950, AG-7600, AG-7000 and AG-1100, which aremanufactured by Asahi Glass Co., Ltd.

The water-dispersing resin to be included in the inkjet ink may be ahomopolymer or a copolymer.

Such a water-dispersing resin is used as an aqueous resin dispersionsuch that a resin having self-dispersing property is dispersed in wateror an aqueous resin dispersion such that a resin is dispersed in waterusing a surfactant. Among these aqueous resin dispersions, resindispersions prepared by subjecting ionomers of polyester resins andpolyurethane resins, or unsaturated monomers to emulsion polymerizationor suspension polymerization can be preferably used.

When preparing resin emulsions by subjecting an unsaturated monomer toemulsion polymerization, methods in which components such as anunsaturated monomer, a polymerization initiator, an emulsifier, a chaintransfer agent, a chelating agent, and a pH controlling agent arereacted in water are typically used. Therefore, aqueous resindispersions can be easily prepared.

Specific examples of unsaturated monomers for use in preparing aqueousresin dispersions include unsaturated carboxylic acids such as acrylicacid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid;monofunctional (meth)acrylates such as methyl methacrylate, ethylmethacrylate, isopropyl methacrylate, n-butyl methacrylate, iso-butylmethacrylate, n-amyl methacrylate, iso-amyl methacrylate, n-hexylmethacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decylmethacrylate, dodecyl methacrylate, octadecyl methacrylate, cyclohexylmethacrylate, phenyl methacrylate, benzyl methacrylate, glycidylmethacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,dimethylaminoethyl methacrylate, methacryloxyethyl trimethyl ammoniumsalt, 3-methacryloxypropyl trimethoxysilane, methyl acrylate, ethylacrylate, isopropyl acrylate, n-butyl acrylate, iso-butyl acrylate,n-amyl acrylate, iso-amyl acrylate, n-hexyl acrylate, 2-ethylhexylacrylate, octyl acrylate, decyl acrylate, dodecyl acrylate, octadecylacrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate,glycidyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate,dimethylaminoethyl acrylate, and acryloxyethyl trimethyl ammonium salt;polyfunctional (meth)acrylates such as ethylene glycol dimethacrylate,diethylene glycol dimethacrylate, triethylene glycol dimethacrylate,polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate,1,4-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate,neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate,polypropylene glycol dimethacrylate, polybutylene glycol dimethacrylate,2,2′-bis(4-methacryloxydiethoxyphenyl)propane, trimethylolpropanetrimethacrylate, trimethylolethane trimethacrylate, polyethylene glycoldiacrylate, triethylene glycol diacrylate, 1,3-butylene glycoldiacrylate, 1,4-butylene glycol diacrylate, 1,6-hexanediol diacrylate,neopentyl glycol diacrylate, 1,9-nonanediol diacrylate, polypropyleneglycol diacrylate, 2,2′-bis(4-acryloxypropiloxyphenyl)propane,2,2′-bis(4-acryloxydiethoxyphenyl)propane, trimethylolpropanetriacrylate, trimethylolethane triacrylate, tetramethylolmethanetriacrylate, ditrimethylolpropane tetraacry late, tetramethylomethanetetraacrylate, pentaerythritol tetraacrylate, and dipentaerythritolhexaacrylate; (meth)acrylamide monomers such as acrylamide,methacrylamide, N,N-dimethylacrylamide, methylenebisacrylamide, and2-acrylamide-2-methylpropane sulfonic acid; aromatic vinyl monomers suchas styrene, α-methylstyrene, vinyl toluene, 4-t-butylstyrene,chlorostyrene, vinyl anisole, vinyl naphthalene, and divinyl benzene;vinyl cyano monomers such as acrylonitrile, and methacrylonitrile; vinylmonomers such as vinyl acetate, vinylidene chloride, vinyl chloride,vinyl ether, vinyl ketone, vinyl pyrrolidone, vinylsulfonic acid andsalts thereof, vinyl trimethoxysilane, and vinyl triethoxysilane; allylcompounds such as allylsulfonic acid and salts thereof, allylamine,allylchloride, diallylamine, and diallyldimethylammonium salts; olefinssuch as ethylene and propylene; diene compounds such as butadiene andchloroprene; and oligomers having unsaturated carbon such as styreneoligomers having a methacryloyl group, styrene-acrylonitrile oligomershaving a methacryloyl group, methyl methacrylate oligomers having amethacryloyl group, dimethylsiloxane oligomers having a methacryloylgroup, and polyester oligomers having an acryloyl group. These monomerscan be used alone or in combination.

The pH of the inkjet ink is generally from 4 to 12 at 25° C., and fromthe viewpoint of miscibility with water-dispersing colorants, the pH ismore preferably 6 to 11, and even more preferably from 7 to 9. When thepH is less than 4 or greater than 12, the aqueous resin dispersionincluded therein tends to be destroyed or subjected to molecular chaincutting such as hydrolysis.

The volume average particle diameter (D50) of the above-mentionedaqueous resin dispersion is generally not less than 50 nm. When thevolume average particle diameter (D50) is less than 50 nm, the viscosityof the aqueous resin dispersion tends to excessively increase, resultingin increase of the viscosity of the resultant inkjet ink. In addition,the volume average particle diameter (D50) of the aqueous resindispersion is generally not greater than 200 nm, and preferably notgreater than 150 nm. When the volume average particle diameter (D50) isgreater than 200 nm, the ejection stability of the resultant inkjet inktends to deteriorate.

Such an aqueous resin dispersion is included in the inkjet ink toenhance the fixability of the colorant in the ink to recording mediasuch as papers. Therefore, the aqueous resin dispersion preferably has aminimum film forming temperature (MFT) of not higher than 30° C.

The water-dispersing resin of the aqueous resin dispersion preferablyhas a glass transition temperature of not lower than −40°. When theglass transition temperature is lower than −40°, the resultant film ofthe resin becomes viscous, and therefore the resultant ink images tendto have tackiness.

The content on a dry basis of such a water-dispersing resin in theinkjet ink is generally from 1% to 15% by weight, and preferably from 2%to 7% by weight, based on the weight of the inkjet ink.

The inkjet ink for use in the present invention can further includeother components such as pH controlling agents, antiseptics/fungicides,chelating agents, anti-rust agents, antioxidants, and ultravioletabsorbents.

The pH controlling agent is not particularly limited as long as the pHcontrolling agent can control the pH of the inkjet ink in a pH range offrom 7 to 11. Specific examples thereof include alcoholamines such asdiethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3-propanediol;hydroxides of alkali metals such as lithium hydroxide, sodium hydroxide,and potassium hydroxide; ammonium hydroxides such as ammonium hydroxide,and quaternary ammonium hydroxide; phosphonium hydroxides such asquaternary phosphonium hydroxide; and carbonates of alkali metals suchas lithium carbonate, sodium carbonate, and potassium carbonate.

Specific examples of the antiseptics/fungicides include sodiumdehydroacetate, sodium sorbate, sodium salt of 2-pilidinethiol-1-oxide,sodium benzoate, and sodium salt of pentachlorophenol.

Specific examples of the chelating agents include sodium ethylenediaminetetraacetate, sodium nitrilotriacetate, sodiumhydroxyethylethylenediaminetriacetate, sodiumdiethylenetriaminepentaacetate, and sodium uramildiacetate.

Specific examples of the anti-rust agents include acidic sulfites,sodium thiosulfate, ammonium thioglycolate, diisopropylammonium nitrite,pentaerythritol tetranitrate, and dicyclohexylammonium nitrite.

Specific examples of the antioxidants include, but are not limitedthereto, phenolic antioxidants such as butylated hydroxyanisole,2,6-di-tert-butyl-4-ethylphenol,stearyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,2,2′-methylenebis(4-methyl-6-tert-butylphenol),2,2′-methylenebis(4-ethyl-6-tert-butylphenol),4,4′-butylidenebis(3-methyl-6-tert-butylphenol),3,9-bis{1,1-dimethyl-2-[β-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]ethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane,1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,1,3,5-trimethyl-2,4-6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,andtetrakis[methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyppropionate]methane;amine type antioxidants such as phenyl-β-naphthylamine, α-naphthylamine,N,N′-di-sec-butyl-p-phenylenediamine, phenothiazine,N,N′-diphenyl-p-phenylenediamine, 2,6-di-tert-butyl-p-cresol,2,6-di-tert-butylphenol, 2,4-dimethyl-6-tert-butylphenol,butylhydroxyanisole, 2,2′-methylenebis(4-methyl-6-tert-butylphenol),4,4′-butylidenebis(3-methyl-6-tert-butylphenol),4,4′-thiobis(3-methyl-6-tert-butylphenol),tetrakis[methylene-3-(3,5-di-tert-butyl-4-dihydroxyphenyl)propionate]methane,and 1,1,3-tris(2-methyl-4-hyroxy-5-tert-butylphenyl)butane;sulfur-containing antioxidants such as dilauryl-3,3′-thiodipropionate,distearyl thiodipropionate, laurylstearyl thiodipropionate,dimyristyl-3,3′-thiodipropionate, distearyl-β,β′-thiodipropionate,2-mercaptobenzoimidazole, and dilauryl sulfide; andphosphorus-containing antioxidants such as triphenyl phosphite,octadecyl phosphite, triisodecyl phosphite, trilauryl trithiophosphite,and trinonylphenyl phosphite.

Specific examples of the ultraviolet absorbents include benzophenonetype ultraviolet absorbents such as 2-hydroxy-4-n-octoxybenzophenone,2-hydroxy-4-n-dodecyloxybenzophenone, 2,4-dihydroxybenzophenone,2-hydroxy-4-methoxybenzophenone, and 2,2′,4,4′-tetrahydroxybenzophenone;benzotriazole type ultraviolet absorbents such as2-(2′-hydroxy-5′-t-octylphenyl)benzotriazole,2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-4′-octoxyphenyl)benzotriazole, and2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole;salicylate type ultraviolet absorbents such as phenyl salicylate,p-tert-butylphenyl salicylate, and p-octylphenyl salicylate;cyanoacrylate type ultraviolet absorbents such asethyl-2-cyano-3,3′-diphenyl acrylate,methyl-2-cyano-3-methyl-3-(p-methoxyphenyl) acrylate, andbutyl-2-cyano-3-methyl-3-(p-methoxyphenyl) acrylate; and nickel complextype ultraviolet absorbents such as nickelbis(octylphenyl) sulfide,2,2′-thiobis(4-tert-octylferrate)-n-butylaminenickel(II),2,2′-thiobis(4-tert-octylferrate)-2-ethylhexylaminenickel(II), and2,2′-thiobis(4-tert-octylferrate)triethanolaminenickel(II).

The method for ejecting the inkjet ink is not particularly limited, andfor example, methods in which stimulus (energy) is applied to the ink inan inkjet recording head to eject the ink from the inkjet recording headcan be used.

In this regard, the inkjet recording head preferably has a configurationsuch that at least one of the liquid chamber, the fluid resistantportion, the vibrating plate and the nozzle includes silicon or nickel.

The nozzle preferably has a diameter of not greater than 30 μm, and morepreferably from 1 μm to 20 μm.

The stimulus applied to the inkjet ink is not particularly limited, andspecific examples thereof include heat (temperature), pressure,vibration, light, and combinations thereof. Among these stimuli, heatand pressure are preferable.

When the stimulus is heat, heat energy is applied to the ink in aninkjet recording head according to image information signals using aresistor to form a bubble in the ink, thereby ejecting the ink in therecording head from a nozzle by the pressure of the bubble.

When the stimulus is pressure, a voltage is applied to a piezoelectricelement adhered to a pressure chamber present in an ink flow path in aninkjet recording head to bend the piezoelectric element, therebydecreasing the volume of the pressure chamber, resulting in ejection ofthe inkjet ink from a nozzle.

The volume of an inkjet ink droplet ejected from a nozzle is generallyfrom 3×10⁻¹⁵ to 40×10⁻¹⁵ m³ (i.e., 3 to 40 pl).

The speed of an ejected ink droplet is generally from 5 to 20 m/s.

The vibration frequency of a piezoelectric element is generally not lessthan 1 kHz.

The resolution of images recorded by ejected ink droplets is generallynot less than 300 dpi (dots per inch).

The inkjet recording method of the present invention preferably includescontrolling using a controller such as sequencers, and computers.

The recording medium on which ink images are formed is not particularlylimited, and specific examples thereof include plain papers, specialpapers, cloths, films, OHP sheets, and general-purpose printing papers.

The inkjet recording method of the present invention can be applied toinkjet printers, inkjet facsimiles, inkjet copiers, inkjetprinter/fax/copier multifunctional products and the like inkjetrecording apparatuses.

An inkjet recording apparatus for use in the inkjet recording method ofthe present invention is illustrated in FIG. 1.

Referring to FIG. 1, an inkjet recording apparatus 100 includes arecording sheet feed tray 101 on which a stack of recording sheets isset, a copy tray 102 on which recording sheets bearing images thereonare stacked, and an ink cartridge setting portion 103 to which inkcartridges 200 are detachably attached. On the upper surface of the inkcartridge setting portion 103, an operating portion 104 includingoperation keys, a display, etc. is arranged. The ink cartridge settingportion 103 has a front cover 103 a which is openable and closable sothat the ink cartridges 200 can be attached to the ink cartridge settingportion 103 or detached therefrom.

As illustrated in FIGS. 2 and 3, a carriage 107 is slidably supported bya guide rod 105 and a stay 106, which are supported by both side plates(not shown) of the inkjet recording apparatus 100, so that the carriage107 is moved in a main scanning direction A by a main scanning motor(not shown) to perform a scanning operation (i.e., image formingoperation).

An inkjet recording head including four inkjet recording heads 108, eachof which has multiple nozzles arranged in a direction perpendicular tothe main scanning direction A to eject droplets of yellow (Y), magenta(M), cyan (C) or black (K) ink downward, is provided on the carriage107.

Each of the four inkjet recording heads 108 includes an energy generatorto eject ink droplets. Specific examples of the energy generatorinclude, but are not limited thereto, piezoelectric actuators (e.g.,piezoelectric devices), thermal actuators to eject ink dropletsutilizing phase change of ink by boiling a liquid film using anelectrothermal device such as a resistor, shape memory alloy actuatorsutilizing phase change of metal caused by temperature change, andelectrostatic actuators utilizing electrostatic force.

In addition, sub-tanks 109 to supply the color inkjet inks to therecording heads 108 are provided on the carriage 107. The color inkjetinks in the ink cartridges 200 set to the ink cartridge setting portion103 are supplied to the respective sub-tanks 109 via respective inksupplying tubes (not shown).

The inkjet recording apparatus includes a recording sheet supplier tofeed recording sheets P set on a sheet loading portion (pressing plate)101 a. The recording sheet supplier includes a sheet feeding roller 110and a separation pad 111, which faces the sheet feeding roller 110 whilebeing biased toward the sheet feeding roller and which is made of amaterial having a high friction coefficient, to feed the recording sheetP one by one from the sheet loading portion 101 a.

The inkjet recording apparatus further includes a feeder to feed therecording sheet P, which has been fed by the recording sheet supplieralong a guide 112, toward an image recording area located below theinkjet recording heads 108. The feeder includes a feeding belt 113 tofeed the recording sheet P while electrostatically attracting therecording sheet, a counter roller 114 to feed the recording sheet P,which is fed from the recording sheet supplier along the guide 112,while sandwiching the recording sheet P with the feeding belt 113, adirection changing guide 115 to change the direction of the recordingsheet P, which is fed substantially vertically, at an angle of about 90°so that the recording sheet P is contacted with the feeding belt 113 soas to be fed thereby, a pressing roller 117 which is biased toward thefeeding belt 113 by a pressing member 116, and a charging roller 118 tocharge the surface of the feeding belt 113.

The feeding belt 113 is an endless belt, which is tightly stretched by afeeding roller 119 and a tension roller 120 so as to be rotated in arecording sheet feeding direction B. In addition, a guide member 121 isarranged below the feeding belt 113 so as to face the recording area inwhich an image is recorded on the recording sheet P by the inkjetrecording heads 108.

The material and configuration of the feeding belt 113 is notparticularly limited. For example, the feeding belt 113 consists of afirst layer (i.e., uppermost layer), which electrostatically attractsthe recording sheet P and which is made of a resin layer (such as atetrafluoroethylene—ethylene copolymer (ETFE) whose electrostaticresistance is not controlled) with a thickness of about 40 μm, and asecond layer (i.e., medium resistance layer or grounding layer), whichis made of almost the same material as that of the first layer exceptthat carbon black is included therein so that the second layer has amedium electric resistance.

The inkjet recording apparatus 100 further includes a sheet dischargerto discharge the recording sheet P bearing an image thereon from themain body of the apparatus. The sheet discharger includes a separationpick 122 to separate the recording sheet P from the feeding belt 113,and discharging rollers 123 and 124 to discharge the recording sheet Ptoward the copy tray 102 located below the discharging roller 123.

A duplex copy unit 125 is detachably attached to the backside of themain body of the inkjet recording apparatus 100. The duplex copy unit125 receives the recording sheet P, which is fed to the duplex copy unitby reversely rotating the feeding belt 113, and feeds again therecording sheet P to the nip between the counter roller 114 and thefeeding belt 113 so that another image is formed on the backside of therecording sheet P by the inkjet recording heads 108 in the recordingarea.

A manual sheet feeder 126, by which a recording sheet can be manuallyfed to the inkjet recording apparatus 100, is provided above the duplexcopy unit 125.

Next, the image forming operation of the inkjet recording apparatus 100will be described.

The recording sheet P is supplied one by one by the recording materialsupplier. The recording sheet P thus fed in substantially the verticaldirection is guided by the guide 112 to the nip between the feeding belt113 and the counter roller 114. The recording sheet P is guided by thedirection changing guide 115 so that the direction of the sheet ischanged at an angle of about 90°. The recording sheet P is then fed bythe feeding belt 113 while pressed toward the feeding belt by thepressing roller 117.

Since the feeding belt 113 is charged by the charging roller 118, therecording sheet P is fed by the feeding belt 113 while electrostaticallyadhered thereto. Next, the carriage 107 is moved in the main scanningdirection A while the inkjet recording heads 108 are driven according toimage signals so as to eject droplets of the inkjet inks to form oneline of image on the surface of the recording sheet P, which is stoppedin the image forming operation. After recording one line of image, therecording sheet P is fed by a predetermined length, and the next imageforming operation is performed to form another one line of image on thesurface of the recording material sheet P. By repeating the imageforming operation, an image is formed on the surface of the recordingmaterial sheet P. When the inkjet recording apparatus 100 receives asignal such that the image recording operation is completed or the rearedge of the recording sheet P reaches the recording area, the inkjetrecording apparatus stops the image forming operation, and the sheetdischarger discharges the recording sheet P bearing the image thereon tothe copy tray 102.

When it is detected that the ink in the sub tank 109 is substantiallyexhausted (i.e., near-end of ink is detected), a predetermined amount ofink is supplied to the sub tank 109 from the corresponding ink cartridge200.

When the ink in the ink cartridge 200 is exhausted, it is possible thatafter the ink cartridge is disassembled, the ink bag in the inkcartridge is replaced with a new ink bag, and then the ink cartridge 200is assembled again to be attached to the inkjet recording apparatus 100.Even when the ink cartridge 200 is set so as to be vertical from a frontside of the inkjet recording apparatus 100 as illustrated in FIG. 1, theink in the ink cartridge 200 can be stably supplied to the correspondingsub tank 109. Therefore, even when the ink cartridge cannot be set fromthe upper side of the inkjet recording apparatus 100 due to spacelimitation (for example, in a case where the apparatus is set in a rackor an object is set on the upper surface of the apparatus), the inkcartridge 200 can be easily replaced.

Hereinbefore, the inkjet recording method of the present invention hasbeen described by reference to a serial (shuttle-type) inkjet recordingapparatus in which a carriage is scanned in the main scanning direction.However, the inkjet recording method of the present invention is notlimited thereto, and can be used for line inkjet recording apparatususing a line-type inkjet recording head.

As illustrated in FIG. 4, the ink cartridge 200 has a configuration suchthat an ink bag 201 containing such an inkjet ink as mentioned above isset in a plastic case 202, and is detachably attachable to the inkjetrecording apparatus 100.

The ink bag 201 is made of a material such as aluminum-laminated filmsand resin films. The inkjet ink is injected into the ink bag 201 from aninlet 201 a. After discharging air from the ink bag 201, the inlet 201 ais closed by welding or the like. The ink bag 201 has an ink outlet 201b made of a rubber. When the ink bag 201 is used, the ink bag is set inan inkjet recording apparatus so that a needle of the inkjet recordingapparatus is inserted into the ink outlet 201 b of the ink bag 201, andthereby the ink in the ink bag 201 can be fed to the sub tank 109.

Having generally described this invention, further understanding can beobtained by reference to certain specific examples which are providedherein for the purpose of illustration only and are not intended to belimiting. In the descriptions in the following examples, the numbersrepresent weight ratios in parts, unless otherwise specified.

EXAMPLES 1. Preparation of Dispersion of Self-Dispersing Black Pigment

Ninety (90) grams of a carbon black having a CTAB specific surface areaof 150 m²/g, and a DBP oil absorption of 100 ml/100 g was added to 3,000ml of a 2.5N aqueous solution of sodium sulfate, and the mixture washeated to 60° C. while agitated for 10 hours by an agitator rotated at aspeed of 300 rpm to perform a reaction. The reaction product wasfiltered, and the obtained carbon black was mixed with an aqueoussolution of sodium hydroxide to neutralize the carbon black, followed byultrafiltration using pure water and a dialysis membrane.

After the carbon black was washed with pure water, the carbon black wasdried. The dried carbon black was dispersed in pure water while fullyagitated to prepare a dispersion of a self-dispersing black pigment,which has a solid content of 30% by weight. The thus prepared carbonblack pigment dispersion had a volume average particle diameter (D50) of103 nm when the volume average particle diameter was measured with aparticle diameter distribution measuring instrument, NANOTRACK UPA-EX150from Nikkiso Co., Ltd.

2. Preparation of Dispersion of Particulate Resin Including MagentaPigment (1) Preparation of Resin Solution

After air inside a 1-liter flask, which is equipped with a mechanicalagitator, a thermometer, a nitrogen gas feed pipe, a reflux tube, and adropping funnel, was substituted with a nitrogen gas, the followingcomponents were fed thereto to prepare a mixture.

Styrene 11.2 g  Acrylic acid 2.8 g Lauryl methacrylate 12.0 g Polyethylene glycol methacrylate 4.0 g Styrene macromer 4.0 gMercaptoethanol 0.4 g

The mixture was heated to 65° C.

Next, the following components were mixed and the mixture was droppedinto the flask over 2.5 hours using the dropping funnel.

Styrene 100.8 g  Acrylic acid 25.2 g Lauryl methacrylate 108.0 g Polyethylene glycol methacrylate 36.0 g Hydroxyethyl methacrylate 60.0 gStyrene macromer 36.0 g Mercaptoethanol  3.6 g Azobismethylvaleronitrile 2.4 g Methyl ethyl ketone 18.0 g

Thereafter, a mixture of 0.8 g of azobismethylvaleronitrile and 18.0 gof methyl ethyl ketone was dropped into the flask over 0.5 hours usingthe dropping funnel.

After the reaction product in the flask was aged for 1 hour at 65° C.,0.8 g of azobismethylvaleronitrile was fed into the flask, and themixture was further aged for 1 hour. Thereafter, 364.0 g of methyl ethylketone was fed into the flask.

Thus, 800 g of a resin solution having a solid content of 50% by weightwas prepared.

(2) Preparation of Dispersion of Particulate Resin Including MagentaPigment

The following components were mixed by agitation.

Resin solution prepared above   28 g C.I. Pigment Red 122   42 g 1Mole/L aqueous solution of potassium hydroxide 13.6 g Methyl ethylketone 20.0 g Pure water 13.6 g

The mixture was kneaded using a roll mill. The thus prepared paste wasfed into 200 g of pure water, and the mixture was fully agitated.Thereafter, methyl ethyl ketone and water were distilled away from themixture using an evaporator to prepare a dispersion. Further, thedispersion was subjected to pressure-filtering using a polyvinylidenefluoride membrane filter having an average pore diameter of 5.0 μm toremove coarse particles. Thus, a dispersion of particulate resinincluding a magenta pigment, which has a pigment content of 15% byweight and a solid content of 20% by weight, was prepared. The volumeaverage particle diameter (D50) of the magenta pigment-containing resinin the dispersion was 127 nm.

3. Preparation of Dispersion of Particulate Resin Including Cyan Pigment

The procedure for preparation of the magenta pigment-containing resindispersion mentioned above was repeated except that the pigment (C.I.Pigment Red 122) was replaced with a cyan pigment (C.I. Pigment Blue15:3) to prepare a cyan pigment-containing resin dispersion. The volumeaverage particle diameter (D50) of the particulate resin in thedispersion was 93 nm.

4. Preparation of Dispersion of Particulate Resin Including YellowPigment

The procedure for preparation of the magenta pigment-containing resindispersion mentioned above was repeated except that the pigment (C.I.Pigment Red 122) was replaced with a yellow pigment (C.I. Pigment Yellow74) to prepare a yellow pigment-containing resin dispersion. The volumeaverage particle diameter (D50) of the particulate resin in thedispersion was 76 nm.

5. Preparation of Inkjet Ink 1

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 10.00 parts 1,3-Butanediol 10.00parts (wetting agent) Glycerin 10.00 parts (wetting agent)2,2,4-Trimethyl-1,3-pentanediol  2.00 parts (penetrant) Polyoxyethyleneperfluoroalkyl ether  2.50 parts (ZONYL FS-300 from Du Pont, serving asa fluorine- containing surfactant including the active ingredient at 40%by weight) Antiseptic  0.05 parts (PROXEL GXL from Avecia Inc. including1,2- benzothiazoline-3-one as a main component in an amount of 20% byweight while including dipropylene glycol) Pure water 30.35 parts

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion POLYSOL ROY6312from Showa Denko K.K., which has a solid content of 37.2%, was added tothe mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the self-dispersing carbon black pigment dispersion preparedabove and 0.10 parts of a self emulsification type silicone defoamingagent (KM-72F from Shin-Etsu Chemical Co., Ltd., including the activeingredient at 100% by weight) were added to the mixture, and the mixturewas agitated for 1 hour. The mixture was subjected to pressure-filteringusing a polyvinylidene fluoride membrane filter having an average porediameter of 5.0 μm to remove coarse particles. Thus, an inkjet ink 1 wasprepared. The inkjet ink 1 had a viscosity of 7.9 mPa·s, and a surfacetension of 23.7 mN/m.

In this regard, the viscosity of an ink was measured at 25° C. using aviscometer RE-80L from Toki Sangyo Co., Ltd., which is rotated at 50rpm. The surface tension of an ink was measured at 25° C. and 50% RHusing a fully automatic surface tensiometer, CBVP-Z from Kyowa InterfaceScience Co., Ltd.

6. Preparation of Inkjet Ink 2

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 18.00 parts 3-Methyl-1,3-butanediol10.00 parts (wetting agent) Glycerin 10.00 parts (wetting agent)2-Ethyl-1,3-hexanediol  2.00 parts (penetrant) Polyoxyethyleneperfluoroalkyl ether  2.50 parts (ZONYL FS-300 from Du Pont, serving asa fluorine- containing surfactant including the active ingredient at 40%by weight) Antiseptic  0.05 parts (PROXEL GXL from Avecia Inc. including1,2- benzothiazoline-3-one as a main component in an amount of 20% byweight while including dipropylene glycol) Pure water 24.35 parts

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion AP-4710 fromShowa Highpolymer Co. Ltd., which has a solid content of 50% by weight,was added to the mixture, and the mixture was agitated for 1 hour.Further, 30.00 parts of the self-dispersing carbon black pigmentdispersion prepared above and 0.10 parts of a self emulsification typesilicone defoaming agent (KM-72F from Shin-Etsu Chemical Co., Ltd.,including the active ingredient at 100% by weight) were added to themixture, and the mixture was agitated for 1 hour. The mixture wassubjected to pressure-filtering using a polyvinylidene fluoride membranefilter having an average pore diameter of 5.0 μm to remove coarseparticles. Thus, an inkjet ink 2 was prepared. The inkjet ink 2 had aviscosity of 8.1 mPa·s, and a surface tension of 23.7 mN/m.

7. Preparation of Inkjet Ink 3

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 15.00 parts3-n-Butoxy-N,N-dimethylpropionamide  5.00 parts 1,3-Butanediol 10.00parts (wetting agent) Glycerin 10.00 parts (wetting agent)2,2,4-Trimethyl-1,3-pentanediol  2.00 parts (penetrant) Polyoxyethylenepolyoxypropylene alkyl ether  1.50 parts (SOFTANOL P-7025 from NipponShokubai Co., Ltd., serving as a surfactant including the activeingredient at 100% by weight) Antiseptic  0.05 parts (PROXEL GXL fromAvecia Inc. including 1,2- benzothiazoline-3-one as a main component inan amount of 20% by weight while including dipropylene glycol) Purewater 21.35 parts

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion POLYSOL ROY6312from Showa Denko K.K., which has a solid content of 37.2%, was added tothe mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the self-dispersing carbon black pigment dispersion preparedabove and 0.10 parts of a self emulsification type silicone defoamingagent (KM-72F from Shin-Etsu Chemical Co., Ltd., including the activeingredient at 100% by weight) were added to the mixture, and the mixturewas agitated for 1 hour. The mixture was subjected to pressure-filteringusing a polyvinylidene fluoride membrane filter having an average porediameter of 5.0 μm to remove coarse particles. Thus, an inkjet ink 3 wasprepared. The inkjet ink 3 had a viscosity of 7.8 mPa·s, and a surfacetension of 25.9 mN/m.

8. Preparation of Inkjet Ink 4

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 10.00 parts3-n-Butoxy-N,N-dimethylpropionamide 10.00 parts 1,3-Butanediol 10.00parts (wetting agent) Glycerin 10.00 parts (wetting agent)2-Ethyl-1,3-hexanediol  2.00 parts (penetrant) Polyoxyethyleneperfluoroalkyl ether  2.50 parts (ZONYL FS-300 from Du Pont, serving asa fluorine- containing surfactant including the active ingredient at 40%by weight) Antiseptic  0.05 parts (PROXEL GXL from Avecia Inc. including1,2- benzothiazoline-3-one as a main component in an amount of 20% byweight while including dipropylene glycol) Pure water 20.35 parts

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion AP-4710 fromShowa Highpolymer Co. Ltd., which has a solid content of 50%, was addedto the mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the dispersion of particulate resin including a magenta pigmentprepared above and 0.10 parts of a self emulsification type siliconedefoaming agent (KM-72F from Shin-Etsu Chemical Co., Ltd., including theactive ingredient at 100% by weight) were added to the mixture, and themixture was agitated for 1 hour. The mixture was subjected topressure-filtering using a polyvinylidene fluoride membrane filterhaving an average pore diameter of 5.0 μm to remove coarse particles.Thus, an inkjet ink 4 was prepared. The inkjet ink 4 had a viscosity of7.9 mPa·s, and a surface tension of 24.7 mN/m.

9. Preparation of Inkjet Ink 5

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 10.00 parts3-n-Butoxy-N,N-dimethylpropionamide 10.00 parts 3-Methyl-1,3-butanediol10.00 parts (wetting agent) Glycerin 10.00 parts (wetting agent)2,2,4-Trimethyl-1,3-pentanediol  2.00 parts (penetrant) Polyoxyethyleneperfluoroalkyl ether  2.50 parts (ZONYL FS-300 from Du Pont, serving asa fluorine- containing surfactant including the active ingredient at 40%by weight) Antiseptic  0.05 parts (PROXEL GXL from Avecia Inc. including1,2- benzothiazoline-3-one as a main component in an amount of 20% byweight while including dipropylene glycol) Pure water 20.35 parts

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion POLYSOL ROY6312from Showa Denko K.K., which has a solid content of 37.2%, was added tothe mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the dispersion of particulate resin including a cyan pigmentprepared above and 0.10 parts of a self emulsification type siliconedefoaming agent (KM-72F from Shin-Etsu Chemical Co., Ltd., including theactive ingredient at 100% by weight) were added to the mixture, and themixture was agitated for 1 hour. The mixture was subjected topressure-filtering using a polyvinylidene fluoride membrane filterhaving an average pore diameter of 5.0 μm to remove coarse particles.Thus, an inkjet ink 5 was prepared. The inkjet ink 5 had a viscosity of7.4 mPa·s, and a surface tension of 23.4 mN/m.

10. Preparation of Inkjet Ink 6

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 10.00 parts 3-n-Butoxy-N,N-dimethylpropionamide 8.00 parts 1,3-Butanediol 10.00parts  (wetting agent) Glycerin 10.00 parts  (wetting agent)2-Ethyl-1,3-hexanediol 2.00 parts (penetrant) Polyoxyethyleneperfluoroalkyl ether 2.50 parts (ZONYL FS-300 from Du Pont, serving as afluorine- containing surfactant including the active ingredient at 40%by weight) Antiseptic 0.05 parts (PROXEL GXL from Avecia Inc. including1,2- benzothiazoline-3-one as a main component in an amount of 20% byweight while including dipropylene glycol) Pure water 22.35 parts 

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion AP-4710 fromShowa Highpolymer Co. Ltd., which has a solid content of 50%, was addedto the mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the dispersion of particulate resin including a yellow pigmentprepared above and 0.10 parts of a self emulsification type siliconedefoaming agent (KM-72F from Shin-Etsu Chemical Co., Ltd., including theactive ingredient at 100% by weight) were added to the mixture, and themixture was agitated for 1 hour. The mixture was subjected topressure-filtering using a polyvinylidene fluoride membrane filterhaving an average pore diameter of 5.0 μm to remove coarse particles.Thus, an inkjet ink 6 was prepared. The inkjet ink 6 had a viscosity of8.0 mPa·s, and a surface tension of 25.3 mN/m.

11. Preparation of Inkjet Ink 7

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 10.00 parts  Glycerin 5.00 parts(wetting agent) 2,2,4-Trimethyl-1,3-pentanediol 2.00 parts (penetrant)Polyoxyethylene perfluoroalkyl ether 3.00 parts (ZONYL FS-300 from DuPont, serving as a fluorine- containing surfactant including the activeingredient at 40% by weight) Antiseptic 0.05 parts (PROXEL GXL fromAvecia Inc. including 1,2- benzothiazoline-3-one as a main component inan amount of 20% by weight while including dipropylene glycol) Purewater 44.85 parts 

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion POLYSOL ROY6312from Showa Denko K.K., which has a solid content of 37.2%, was added tothe mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the self-dispersing carbon black dispersion prepared above and0.10 parts of a self emulsification type silicone defoaming agent(KM-72F from Shin-Etsu Chemical Co., Ltd., including the activeingredient at 100% by weight) were added to the mixture, and the mixturewas agitated for 1 hour. The mixture was subjected to pressure-filteringusing a polyvinylidene fluoride membrane filter having an average porediameter of 5.0 μm to remove coarse particles. Thus, an inkjet ink 7 wasprepared. The inkjet ink 7 had a viscosity of 3.5 mPa·s, and a surfacetension of 29.0 mN/m.

12. Preparation of Inkjet Ink 8

The following components were mixed.

3-Methoxy-N,N-dimethylpropionamide 10.00 parts3-n-Butoxy-N,N-dimethylpropionamide 10.00 parts 3-Methyl-1,3-butanediol10.00 parts (wetting agent) Glycerin 10.00 parts (wetting agent)2-Ethyl-1,3-hexanediol  2.00 parts (penetrant) Polyoxyethylenepolyoxypropylene alkyl ether  0.30 parts (SOFTANOL P-7025 from NipponShokubai Co., Ltd., serving as a surfactant including the activeingredient at 100% by weight) Antiseptic  0.05 parts (PROXEL GXL fromAvecia Inc. including 1,2- benzothiazoline-3-one as a main component inan amount of 20% by weight while including dipropylene glycol) Purewater 22.55 parts

The mixture was agitated for 1 hour.

Next, 5.00 parts of an acrylic-silicone resin emulsion AP-4710 fromShowa Highpolymer Co. Ltd., which has a solid content of 50%, was addedto the mixture, and the mixture was agitated for 1 hour. Further, 30.00parts of the self-dispersing carbon black dispersion prepared above and0.10 parts of a self emulsification type silicone defoaming agent(KM-72F from Shin-Etsu Chemical Co., Ltd., including the activeingredient at 100% by weight) were added to the mixture, and the mixturewas agitated for 1 hour. The mixture was subjected to pressure-filteringusing a polyvinylidene fluoride membrane filter having an average porediameter of 5.0 μm to remove coarse particles. Thus, an inkjet ink 8 wasprepared. The inkjet ink 8 had a viscosity of 7.8 mPa·s, and a surfacetension of 33.5 mN/m.

The thus prepared inkjet inks 1-8 were evaluated with respect to thefollowing properties.

1. Contact Angle

The contact angle θ of an inkjet ink was measured at 25° C. and 50% RHusing an automatic contact angle measuring instrument OCAH200 from DataPhysics Corp. Specifically, 2.5 μl of an ink was dropped on a plainpaper, and the contact angle of the ink droplet was measured 0.1 secondslater using the instrument. In this regard, MY PAPER from NBS RicohBusiness Expert, Ltd. which is referred to as a plain paper 1; arecycled paper 100 from Daio Paper Corp. which is referred to as a plainpaper 2; and HAMMERMILL FORE MP from International Paper Company whichis referred to as a plain paper 3 were used as the plain paper.

2. Surface Tension

The surface tension γ of an inkjet ink was measured at 25° C. and 50% RHusing an automatic surface tensiometer CBVP-Z from Kyowa InterfaceScience Co., Ltd.

The results are shown in Table 1 below.

TABLE 1 Plain Plain Plain paper 1 paper 2 paper 3 Surface Contact γcosθContact Contact Inkjet tension γ angle θ (mN/ angle θ γcosθ angle θγcosθ ink (mN/m) (°) m) (°) (mN/m) (°) (mN/m) 1 23.7 30.8 20.4 41.9 17.631.3 20.3 2 23.7 27.7 21.0 35.7 19.2 27.1 21.1 3 25.9 28.6 22.7 40.419.7 28.4 22.8 4 24.7 33.5 20.6 45.6 17.3 35.6 20.1 5 23.4 32.4 19.843.5 17.0 31.9 19.9 6 25.3 34.7 20.8 46.7 17.4 36.5 20.4 7 28.0 15.926.9 31.1 24.0 23.7 25.6 8 33.5 31.1 28.7 47.3 22.7 31.3 28.6

Examples 1-21 and Comparative Examples 1-3

Ink images of each inkjet ink were formed on each of the plain papers1-3 under environmental conditions of 23.5±0.5° C. and 50±5% RH using aninkjet printer IPSIO G717 from Ricoh Co., Ltd. In this regard, thedriving voltage of the piezoelectric element of the printer wascontrolled so that the amounts of inks adhered to the plain papers arethe same.

The evaluation items and the image forming operations therefor were asfollows.

1. Image Density

A copy of a chart having a solid square image with a size of 64 point,which is prepared using Microsoft Word 2000, was formed on each of theplain papers 1-3 using each of the inks 1-8. The image density of thesolid square image was measured with a densitometer X-RITE 939 fromX-Rite Inc. In this regard, the printing mode was set to a mode which isa “plain paper-standard and fast” mode modified so as not to besubjected to color compensation using a driver attached to the printer.

The image density was graded as follows.

-   ◯ (Good): Not lower than 1.2 for black image    -   Not lower than 0.8 for yellow image    -   Not lower than 1 0 for magenta image    -   Not lower than 1.0 for cyan image-   Δ (Acceptable): Not lower than 1.15 and lower than 1.2 for black    image    -   Not lower than 0.75 and lower than 0.8 for yellow image    -   Not lower than 0.95 and lower than 1.0 for magenta image    -   Not lower than 0.95 and lower than 1.0 for cyan image-   × (Bad): Lower than 1.15 for black image    -   Lower than 0.75 for yellow image    -   Lower than 0.95 for magenta image    -   Lower than 0.95 for cyan image

2. Blurring of Character Images

A copy of a chart having character images with a size of 12 point, whichis prepared using Microsoft Word 2000, was formed on each of the plainpapers 1-3 using each of the inks 1-8. In this regard, the printing modewas set to a mode which is a “plain paper-standard and fast” modemodified so as not to be subjected to color compensation using a driverattached to the printer.

The copies were visually observed to determine whether the characterimages are blurred. The blurring was graded as follows.

-   ◯ (Good): The character images are not blurred.-   Δ (Acceptable): The character images are slightly blurred.-   × (Bad): The character images are blurred.

The evaluation results are shown in Tables 2-4 below.

TABLE 2 X + γcosθ Content Content Y Inkjet Plain (mN/ of X* of Y** (wtImage Blur- ink paper m) (wt %) (wt %) %) density ring Ex. 1 1 1 20.4 100 10 Δ ◯ Ex. 2 2 1 21.0 18 0 18 ◯ ◯ Ex. 3 3 1 22.7 15 5 20 ◯ ◯ Ex. 4 4 120.6 10 10 20 ◯ ◯ Ex. 5 5 1 19.8 10 10 20 ◯ ◯ Ex. 6 6 1 20.8 10 8 18 ◯ ◯Comp. 7 1 26.9 10 0 10 ◯ X Ex. 1 Comp. 8 1 28.7 10 10 20 ◯ X Ex. 2 Thecontent of X*: The content of 3-methoxy-N,N-dimethylpropionamide. Thecontent of Y**: The content of 3-n-butoxy-N,N-dimethylpropionamide.

TABLE 3 X + γcosθ Content Content Y Inkjet Plain (mN/ of X of Y (wtImage Blur- ink paper m) (wt %) (wt %) %) density ring Ex. 7 1 2 17.6 100 10 Δ ◯ Ex. 8 2 2 19.2 18 0 18 ◯ ◯ Ex. 9 3 2 19.7 15 5 20 ◯ ◯ Ex. 10 42 17.3 10 10 20 ◯ ◯ Ex. 11 5 2 17.0 10 10 20 ◯ ◯ Ex. 12 6 2 17.4 10 8 18◯ ◯ Ex. 13 7 2 24.0 10 0 10 ◯ Δ Ex. 14 8 2 22.7 10 10 20 ◯ Δ

TABLE 4 X + γcosθ Content Content Y Inkjet Plain (mN/ of X of Y (wtImage Blur- ink paper m) (wt %) (wt %) %) density ring Ex. 15 1 3 20.310 0 10 Δ ◯ Ex. 16 2 3 21.1 18 0 18 ◯ ◯ Ex. 17 3 3 22.8 15 5 20 ◯ ◯ Ex.18 4 3 20.1 10 10 20 ◯ ◯ Ex. 19 5 3 19.9 10 10 20 ◯ ◯ Ex. 20 6 3 20.4 108 18 ◯ ◯ Ex. 21 7 3 25.6 10 0 10 ◯ Δ Comp. 8 3 28.6 10 10 20 ◯ X Ex. 3

It is clear from Tables 2-4 that the inkjet recording methods ofExamples 1-21 can produce high density images on plain papers withoutcausing blurring. In contrast, blurred images are formed by the methodsof Comparative Examples 1-3 because γ cos θ (26.9 mN/m, 28.7 mN/m, and28.6 mN/m in Comparative Examples 1-3) is greater than 26.

Additional modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced other than as specifically described herein.

What is claimed is:
 1. An inkjet recording method comprising: ejectingan inkjet ink toward a recording medium to form an ink image on therecording medium, wherein the inkjet ink includes a pigment, water, asurfactant, and a compound having the following formula (1):CH₃OCH₂CH₂CON(CH₃)₂   (1), and the inkjet ink optionally includesanother compound having the following formula (2):CH₃CH₂CH₂CH₂OCH₂CH₂CON(CH₃)₂   (2), and wherein the inkjet recordingmethod satisfies the following relation:16≦γ cos θ≦26, wherein γ represents a surface tension of the inkjet inkin units of mN/m, and θ represents an angle of contact of the inkjet inkwith the recording medium in units of degree measured 0.1 seconds afterdropping an droplet of the inkjet ink with a volume of 2.5 μl on therecording medium.
 2. The inkjet recording method according to claim 1,wherein the surfactant is a fluorine-containing surfactant.
 3. Theinkjet recording method according to claim 1, wherein the inkjet inkincludes the compound having formula (1) and the optional compoundhaving formula (2) in a total amount of from 10% by weight to 20% byweight.
 4. The inkjet recording method according to claim 1, wherein thepigment is a pigment having a self-dispersing property.
 5. The inkjetrecording method according to claim 1, wherein the inkjet ink furtherincludes at least one of glycerin, 1,3-butanediol, and3-methyl-1,3-butanediol.
 6. The inkjet recording method according toclaim 1, wherein the inkjet ink further includes at least one of apolyol having 8 to 11 carbon atoms, and a polyol ether having 8 to 11carbon atoms.
 7. The inkjet recording method according to claim 6,wherein the inkjet ink includes a polyol having 8 to 11 carbon atoms,and wherein the polyol includes 2-ethyl-1,3-hexanediol or2,2,4-trimethyl-1,3-pentanediol.